0452-B4
Ong Kian Huat 1 , Lim Meng Tsai 1 , Jugah Kadir 2 and Kamis Awang 1
Site characteristics and foliar nutrients of Azadirachta excelsa plantations in relation to growth were studied in Peninsular Malaysia. Slope, in association with soil depth had the greatest influence on the stand growth. Concentrations of N, P, K and Mg in the foliage were sufficient for tree growth. Calcium foliar concentration was been found to be deficient. Foliar concentration of N and K were positively correlated with soil nutrient concentration. The growth parameters were negatively correlated with slope and soil exchangeable K (r > 0.80, P < 0.001). Proper site selection and fertilizer applications are important factors to be considered when establishing A. excelsa stands.
In 1982, Forestry Department of Peninsular Malaysia launched Forest Plantation Compensatory Project to cover 188,200 ha by the year 1995 with 15-year rotation. However, Peninsular Malaysia already started to experience timber shortage in early 1990's (Ismail 1996) and Shaharuddin (1999) projected that Peninsular Malaysia would still face wood shortage for a number years to come even when wood from existing plantation (including Hevea brasiliensis) were considered. Establishing forest plantation is one of the solutions for this crisis. Many countries (e.g. Chile and New Zealand) have already turned to forest plantations for timber production.
In the mid 1990's the Malaysian government began promoting several tree species for forest plantations, one of which is Azadirachta excelsa. Azadirachta excelsa (Meliaceae) is indigenous to the country and has a number of uses including for furniture and home construction due to its high quality timber and wood colour (Anon 1992). Additionally, its young shoots are edible and are used as vegetables (Corner 1940). Ermel et al. (1991) also reported that marrangin and azadirachtin extracted from A. excelsa had insecticidal properties.
However, there is relatively little information on A. excelsa and most of them are from Thailand. An early trial by the Forestry Department of Peninsular Malaysia showed that the growth rate of A. excelsa at three years is comparable to Acacia mangium (Zulkifli and Yahaya 1997). However, the species was reported to perform poorly on N and P deficient soils (Ong 1995), under shade (Sofia 1999), water stress (Jerry 1997) and on compacted soils (Jusnani 1999).
Information on growth under different management regime and establishment methods and different sites are needed for A. excelsa. In 2001, it was estimated that more than 5,000 ha of A. excelsa plantation has already been established in Peninsular Malaysia mainly by small holders (Ong T.H. pers. comm.). However, the potential impact caused by different site management practices on yield and over successive rotations is unknown. Thus, the objective of this study was to examine how the growth of A. excelsa in Peninsular Malaysia relates to foliar nutrient status and soil properties. This information is essential for tree management and fertilizer prescriptions for A. excelsa plantation under similar conditions.
The experiment was conducted in the state of Terengganu and Johore, Malaysia (Figure 1). The altitudes of the sites are below 30 m whilst the soils are sandy clay loam. Both plantations were about two years old when the measurement was carried out.
Figure 1: Location of study sites in Peninsular Malaysia
The plantation in Terengganu is located about 10 km south of Sungai Tong town (5 o 21'N and 102 o 53'E). The average annual temperature varies from 25.0 to 26.9 o C while the mean annual precipitation is 1,882 mm. The plantation was established following clear cutting of first rotation mature old palm stand in July 1997. The site is hilly with slopes of gradient ranging between 0 and 35%. The trees were planted at a spacing of 2.0 x 4.0 m. Fertilizer (200 g per tree with 15(N)-15(P)-15(K)) was applied in April 1999. Weeds were manually removed annually during the two years of this study.
The plantation in Johore is located about 9 km south of Labis town (2 o 21'N and 103 o 02'E). The average annual temperature varies from 25.3 to 26.8 o C while the mean annual precipitation is 2,124 mm. The plantation was established following clear cutting of two rotations of rubber in March 1998. The site was undulating with slope gradient ranging between 0 and 50%. The trees were planted at a spacing of 2.0 x 2.0 m. Seedlings were fertilized at the time of planting with 50 g of 15(N)-15(P)-15(K). Operational schedules for application of fertilizers are presented in Table 1. Weeds were cleared by herbicide application each time before fertilization, leaving no ground cover for most of the time. Thinning of small trees was carried out in December 1999.
Table 1: Fertilization schedule at the Sungai Karas plantation
Age (months) |
Month |
Fertilizer application rate (g tree -1 ) |
0 |
50 g N(15)-P(15)-K(15) | |
1 |
April 2000 |
50 g N(15)-P(15)-K(15) |
5 |
August 2000 |
50 g N(15)-P(15)-K(15) |
9 |
January 2001 |
50 g N(15)-P(15)-K(15) |
13 |
May 2001 |
50 g N(15)-P(15)-K(15) |
17 |
September 2001 |
100 g N(15)-P(15)-K(15) |
21 |
January 2002 |
100 g N(15)-P(15)-K(15) |
In both stands, six representative plots of 0.1 ha were selected and the diameter at breast height (dbh) and total height of all trees in the plot were measured. The measurement was carried out in November 1999 in Sungai Tong plantation and in June 2002 in Sungai Karas plantation. The volume calculation formula was obtained from 42 harvested trees (Ong, unpublished data).
log volume = -3.026 + 1.799(log dbh) + 0.994 (log total height)
Sampling was only carried out in the Sungai Karas plantation. Five soil samples were collected at random from the upper 10 cm soil layer from each plot. The samples were air-dried and sieved with 2 mm screen before analysis. Particle-size analysis was determined using the pipette method. pH was determined by using a 1:2.5 soil/water solution and a glass electrode pH-meter. The total organic C was determined by using the Walkley and Black method (1934) while total N was determined by a Kjeldahl digest (Forster 1995). Available P was determined colorimetrically using the molybdenum-blue method on a Mehlich III extract (John 1970). Exchangeable K, Ca and Mg were determined by atomic absorption spectrophotometer on Mehlich III extracts.
Foliar sampling was carried out in August 2000. Ten trees from each plot were randomly selected for foliar nutrient analysis. Two small branches on upper canopy of each tree were collected. Mature leaves were bulked to give a composite sample. The sample were oven-dried (70 o C) for 48 h, ground and digested with sulphuric acid and hydrogen peroxide (wet digestion method). Nitrogen and P were determined by the similar colorimetric method used for soil. Potassium, Mg and Ca in the digest were determined by atomic absorption spectrophotometry.
Ten slope readings were determined for each plot and then classified into classes of 10% interval. Differences between trees from the different locations were tested for significance using t-test. Correlation and multiple linear regression analyses were used to examine the relationship among soil properties, foliar nutrients and tree growth.
Performance of stands
Growth data of two-year-old trees in the Sungai Tong and Sungai Karas plantations are shown in Table 2. The survival rates in both plantations were about 87%. The trees in the Sungai Karas stand were significantly bigger and taller that those in the Sungai Tong stand. The differences may due to different site preparation, management practices and climate. The increments in growth parameters were similar to those reported by Zulkifli and Yahaya (1997) for a trial at Relai Forest Reserve, Kelantan. At 38 months, A. excelsa stand in Kelantan recorded a mean height of 9.3 m and dbh of 7.4 cm. In a 41-years-old plantation at Bukit Lagong Forest Reserve, Selangor, which was once left unmanaged for a few years, Ahmad Zuhaidi and Weinland (1995) reported a mean height of 26.0 m and dbh of 34.9 cm.
Table 2: Characteristics of the two-year old Azadirachta excelsa stands
Sungai Tong |
||
Altitude (m) |
< 50 |
< 50 |
Age (month) |
27 |
26 |
Slope (%) |
0 - 35 |
0 - 50 |
Diameter breast height (cm) |
4.44 a |
5.77 b |
Total height (m) |
4.17 a |
6.71 b |
Volume (m 3 ha -1 ) |
6.76 a |
38.02 b |
Basal area (m 2 ha -1 ) |
2.02 a |
6.80 b |
Survival (%) |
86.9 |
87.7 |
Significant differences in means are indicated with different letters, a < b (t-test, P < 0.001).
Soil properties and foliar nutrient concentrations
The soil in Sungai Karas is a sandy clay loam and low in pH (Table 3). Based on a fertility rating by Kanapathy (1976) the site is low in exchangeable K and Mg and moderate in organic C, N and P, indicating the current rate of application of fertilizer may still be insufficient to increase the soil fertility. This may be due to the very low existing soil fertility before planting or a high rate of loss through leaching, erosion or tree uptake. Use of fertilizers in the area under the previous crop (Adams, 1984) and the high rainfall could have resulted in the low pH. Low soil pH is often associated with high concentration of exchangeable Al. Liming or ashing maybe needed to increase the soil pH and so lower the concentration of exchangeable Al which maybe toxic to plants.
Table 3: Growth, soil properties and foliar nutrient concentrations of the two-year old Azadirachta excelsa at the Sungai Karas plantation
Parameter |
Mean (standard deviation) |
Diameter breast height (cm) |
5.77 (0.55) |
Total height (m) |
6.71 (0.97) |
Volume (m 3 ha -1 ) |
38.02 (9.88) |
Slope (rank) |
2 |
Sand (%) |
53.03 (12.29) |
Clay (%) |
31.75 (7.82) |
Silt (%) |
15.22 (6.01) |
PH |
3.61 (0.06) |
Organic C (%) |
2.30 (0.53) |
Total N (%) |
0.24 (0.06) |
C/N |
10.19 (4.04) |
Extractable P (mg kg -1 ) |
5.18 (5.21) |
Exchangeable K (ppm) |
173.15 (9.45) |
Exchangeable Mg (ppm) |
15.61 (8.98) |
Exchangeable Ca (ppm) |
46.07 (21.80) |
Exchangeable Al (ppm) |
958.05 (83.34) |
Foliar N (mg g -1 ) |
31.12 (11.67) |
Foliar P (mg g -1 ) |
2.35 (0.59) |
Foliar K (mg g -1 ) |
18.30 (6.38) |
Foliar Mg (mg g -1 ) |
3.61 (1.64) |
Foliar Ca (mg g -1 ) |
2.55 (1.36) |
Except for Ca, other foliar nutrient concentrations (Table 3) were in the range previously reported by Ong et al. (2002) for A. excelsa seedlings grown on Rengam soil series in a glasshouse study. Calcium concentration in the foliage was less than 3.5 mg g -1 , the level considered to be the limiting for A. excelsa. Concentrations of P, Mg and K (which was higher for the latter element) were at the maximum level as compared to study by Ong et al. (2002). Studies have shown that the presence of Al in the soil solution increased tree uptake of K and reduced Ca (Ryan et al. 1986; Huang and Bacherlard 1993).
Relationships among growth parameters, soil properties and foliar nutrient concentrations: correlation analyses
Table 4 shows the coefficients of correlation between growth parameters and soil properties. The dbh was negatively correlated with slope, silt and K, whereas it was positively correlated with sand, pH and Mg. The height and volume were negatively correlated with slope, N and K, whereas they were positively correlated with C/N. On the other hand, foliar concentration of Ca was significantly correlated with all the growth parameters whilst P was positively correlated with height and volume.
Table 4: Coefficients of correlation between soil properties, foliar concentrations and growth parameters
DBH |
Height |
Volume | |
Slope |
-0.91 |
-0.92 |
-0.91 |
Silt |
-0.44 |
||
Total N |
-0.41 |
||
Exchangeable K |
-0.56 |
-0.55 | |
Foliar P |
0.45 |
||
Foliar Ca |
0.64 |
0.56 |
0.65 |
| All figures are significant at P < 0.01. |
Regression equations relating soil properties and foliar nutrient concentrations to growth parameters were obtained (Table 5). Height and volume were influenced by slope, whilst dbh was influenced by N and K. The regression models were highly significant (r 2 > 0.80, P > 0.001).
Table 5: Multiple regressions equation relating soil properties and foliar nutrient concentrations to growth a
Regression equation |
R 2 | |
Soil properties |
DBH = 28.569 + 2.909N - 0.139K |
0.985 |
Height = 7.917 - 0.558Slo |
0.849 | |
Volume = 0.019 - 0.002Slo |
0.829 | |
All |
DBH = 17.071 + 0.277pH - 0.076K - 0.012fN + 0.086fCa |
0.999 |
Height = 9.773 - 0.007C/N - 0.558Slo - 0.001Al - 0.095fMg |
0.999 | |
Volume = 0.019 - 0.002Slo |
0.829 |
| a N: soil total N, K: soil exchangeable K, Slo: slope, fN: foliar N, f Ca: foliar Ca, C/N: soil C to N ratio, Al: soil exchangeable Al, fMg: foliar Mg. |
From the above relationships, it can be seen that the soil characteristics that best explain the differences in growth are slope (for height and volume) and K (for dbh). When considered together, foliar concentration of Ca (for dbh) also had some influence on tree growth.
The poor growth could be due to shallow soil on steep slopes which in turn contribute to a restricted volume for root growth and subsequently the lower availability of water and nutrients. At the higher slope class (41 - 50%), in the study site, the depth of soil is very shallow and stony. Positive relationships between tree growth and soil depth have previously been reported for P. radiata (Louw 1991; Sánchez-Rodríguez et al. 2002).
A negative relationship between dbh and K could be an indirect effect. Higher level of K can reduce the uptake of Ca, which is indicated by the low Ca concentration in the foliage, which subsequently lead to reduce growth of the trees.
Growth of two-year-old A. excelsa is very encouraging even though they are established on acidic soils relatively low in available nutrients. The growth of young A. excelsa stand was found to be strongly influenced by slope (or soil depth) and soil nutrient availability (especially K). Azadirachta excelsa should not be planted on steep slope with shallow soils as growth will be restricted. The level and type of fertilizer applied and the methods of reducing nutrient loss are among the factors that need to be taken into consideration when managing site productivity of A. excelsa plantation especially on acidic sandy clay loam low in available nutrients.
The authors thank Mr. Phoon Ah Kow, the owner of the plantation for access. We also like to thank Mr. Tey Ah Lim, Dr. K.S. Baskaran, Mr. Ong Tai Hock, Mr. Abdul Razak Sulong, Mr. Zakaria Taha, Mr. Salim Ahmad, Mr. Mohamed Yusof Yaacob and Mr. Abdul Latib Senin for the technical help. Funding for this research was through a short-term grant (Grant No. 50204 to Dr. Kamis Awang) from Universiti Putra Malaysia and IRPA grant (Grant No. 01-02-04-0056-EA001 to Dr. Jugah Kadir) from Ministry of Science, Technology and Environment of Malaysia.
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1 Faculty of Forestry, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor
2 Faculty of Agriculture, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor
Corresponding author: Ong Kian Huat
Complete address: Mr. Ong Kian Huat, Faculty of Forestry, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia.
Telephone No.: 603 89467233
Fax No.: 603 89432514
E-mail address: [email protected]
Author: Lim Meng Tsai Email address: [email protected]
Author: Jugah Kadir Email address: [email protected]
Author: Kamis Awang Email address: [email protected]